1. Field of the Invention
The present invention relates to a power converter device such as a 2-level inverter, a 2-level converter, etc. for executing power conversion between a direct current (DC) and a 2-level alternating current (AC) and, more particularly, a technology of reducing internal inductances of the power converter device.
2. Description of the Prior Art
FIG. 18 shows a power converter device set forth in Patent Application Publication (KOKAI) Hei 6-225545, for example, and more particularly a main circuit of a 2-level power converter device which converts DC power into three-phase AC power. In FIG. 18, a reference 10 denotes a capacitor serving as a DC voltage source, and references 1 to 6 denotes switching elements SW1 to SW6 which are connected to form a bridge circuit. The switching elements SW1 to SW6 consist of IGBTs (Insulated Gate Bipolar Transistors) 1A to 6A and fly wheel diodes 1B to 6B which are connected in inverse-parallel with the IGBTs lA to 6A respectively. References 7 to 9 are AC output terminals respectively.
Since a normal circuit operation of the power converter device of this type has been well known, its explanation will be omitted herein. However, induced voltages each of which is defined by a product of a current change rate di/dt which is caused by a turn-off operation of each switching device and an inductance which exists in the circuit wiring become an issue particularly. That is to say, these induced voltages would reduce a breakdown voltage of the switching device. As the measure to overcome the issue, normally such a method has been adopted that the so-called snubber circuit is provided to consume the electromagnetic energy which is generated by the inductance of the circuit. In this case, if the inductance is increased larger, a capacity of a capacitor constituting the snubber circuit is also increased correspondingly. Thus, bad effects such that the power converter device is increased in size to thus increase its loss, etc. have been caused.
As for this respect, in the above Patent Application Publication, inductances of the circuit wirings, especially an inductance Lsa of a wiring, which connects a positive terminal of a capacitor 10 and an anode terminal of a switching device SW1, and an inductance Lsb of a wiring, which connects a negative terminal of a capacitor 10 and a cathode terminal of a switching device SW2, have been watched with interest. Then, the circuit wirings provided in such areas have been formed by a pair of conductive plates and a spacing plate, which is formed of high dielectric-constant material and inserted between the pair of conductive plates, to thus achieve reduction of the inductances.
Since reduction of the inductances has been made as mentioned above in the power converter device in the prior art, a satisfactory effect has not always been achieved in the event that a larger capacity of the switching device, an increase in a switching frequency, etc. are requested. In other words, though described in detail later, overall current paths including the switching devices, which range from the positive terminal P of the DC voltage source to the negative terminal N of the same must be grasped as the subject of study, and then a configuration which is able to minimize the inductance of such overall current paths must be studied.